1. Field of the Invention
The present invention pertains to devices for determining the concentration of gas and, more particularly, to a system that employs ultrasound to determine gas concentration.
2. Description of the Prior Art
Ethylene oxide ("EtO") is commonly used as the sterilizing agent in gas sterilizers. As the sterilization cycle proceeds, it is necessary to monitor the concentration of EtO within the sterilization chamber to ensure that the proper sterilization sequence is occurring and to correct any departures from the standard sterilization cycle. Further, the effectiveness of EtO as a sterilizing agent is optimized, and, hence, the time consumed by the sterilization cycle is minimized, when the relative humidity within the sterilization chamber is maintained between 20 and 40 percent. Therefore, there exists the need for a device that can accurately measure the concentration of EtO and water vapor within a sterilization chamber.
Several types of systems for measuring gas concentration are known. Gas chromatography systems offer good sensitivity and reliability, but are relatively expensive. Infrared spectroscopy provides low sensitivity, low dynamic range and requires a relatively high degree of maintenance. Solid-state sensors are highly sensitive and relatively inexpensive, but cannot measure the concentration of a single gas within a chamber that contains multiple gases.
Therefore, there exists the need for a system for determining the concentration of each of multiple gases present within a chamber that is both highly sensitive and relatively inexpensive.